A radioimmunoassay for catecholamines is described in U.S. Pat. No. 3,704,282. The antigen utilized for eliciting the needed catecholamine specific antibody was prepared by directly coupling the catecholamine to the protein or polypeptide immunogenic carrier using a carbodiimide coupling agent. The resulting antigen is formed by an amide bond linkage of the amine group of the catecholamine with pendant carboxy groups of the support materials. However, the antibody elicited by use of such antigens suffers from a lack of specificity with respect to the critical ethylamine side chain.
Faraj et al., in a paper appearing Pharmacologist, June 1974, describe the preparation of an antibody specific to tyramine. The antigen used for eliciting this antibody is prepared by coupling p-aminohippuric acid to methylated bovine serum albumin followed by diazotization of the amino group and reaction of the diazonium intermediate with tyramine. U.S. Pat. No. 3,690,834 teaches the preparation of antigens and antibodies to a large number of biologically active compounds. The antigens are prepared by linking the compounds to a protein carrier through a suitable linkage. These antigens may then be used to elicit antibodies by conventional procedures. The antibodies and spin-labeled derivatives of the biologically active compounds are then used in an assay procedure. One of the class of active compounds disclosed is the amphetamines (column 9, line 54 to column 10, line 4).